Interpretive Summary: Apple bruising frequently occurs during harvest, postharvest handling, transport and retailing, and it is of great concern because bruised apples can be downgraded or even rejected by consumers, which would result in economic loss to growers, packers, shippers or retailers. Hence preventing or minimizing bruise occurrence at various harvest and postharvest operations is of utmost importance. Moreover, it is also critical to have an effective inspection system to segregate apples with quality-degrading bruises from those free of bruises during packing operations. Research was conducted, using a hyperspectral imaging-based spatially resolved technique recently developed in our lab, to determine the optical absorption and scattering properties of normal and bruised tissue in 'Golden Delicious' and 'Red Delicious' apples and quantify their changes over a period of three weeks. Absorption for the normal, unbruised tissue for 'Golden Delicious' apples was not markedly different from that for the bruised tissue in the spectral region of greater than 600 nm (or 650 nm for 'Red Delicious'). On the other hand, scattering for the unbruised tissue was significantly higher than that for the bruised tissue for the wavelengths of 500-1,000 nm; its value for the bruised tissue decreased consistently over time. Bruising had a more profound effect on scattering than on absorption. This suggests that an optical inspection system that enhances scattering features would be more suitable for detection of bruises on apples. This research provided new knowledge of the optical properties of normal and bruised apples, which will be valuable to researchers and engineers in the development of an effective optical method to detect apple bruises.

Technical Abstract:
Knowledge of the spectral absorption and scattering properties of apple tissue, especially bruised tissue, can help us develop an effective method for detecting bruises during postharvest sorting and grading. This research was intended to determine the optical properties of normal and bruised apple tissue for the spectral range of 500-1,000 nm and quantify their changes with time after bruising. Spectral absorption and reduced scattering coefficients were determined from the normal or unbruised tissue of ‘Golden Delicious’ and ‘Red Delicious’ apples and then the bruised tissue at different time intervals after bruising, using a hyperspectral imaging-based spatially resolved technique. The absorption coefficient for the normal tissue of ‘Golden Delicious’ apples at wavelengths greater than 600 nm (or 650 nm for ‘Red Delicious’), on average, was not markedly different than that for the bruised tissue. The reduced scattering coefficient for the normal apple tissue, however, was much higher than that for the bruised tissue; it decreased consistently with time after bruising. These results suggest that bruising has greater impact on scattering than on absorption. Hence an optical system that enhances the scattering features measurement would be better suited for bruise detection.